Re: [LARTC] Changing default route for an entire subnet/NIC

[Brian Weaver]

Oops, made a mistake in my example,
I actually enter
ip rule add from 192.168.0.0/24 table John

As soon as I do this, that subnet loses all contact with my firewall, so it can't DHCP 
an address,
do DNS servers, ping, anything.. 

Any clues?


[EMAIL PROTECTED] [EMAIL PROTECTED] [2003-12-17 22:34:14 -0700]:
 Greetings,
 
 If you look at Section 4.1 of the howto, they give  asimple example of changing the 
 default
 route for a single IP address by doing the following
 
 # echo 200 John  /etc/iproute2/rt_tables
 # ip rule add from 10.0.0.10 table John
 # ip route add default via 195.96.98.253 dev ppp2 table John
 # ip route flush cache
 
 I'm trying to do something very similar, except that I want to route an entire class 
 C subnet
 out a different NIC card in my firewall..
 
 I did the exact same thing as above except used the line
 
 ip rule add from 192.168.0.1/24 table John
 ip route add default via 192.168.1.1 dev eth4 table John
 
 This doesn't work, what happens is that the entire subnet loses conect with the 
 firewall, so DNS
 lookups fail and I basically can't go anywhere. Using just one IP like the example 
 above seems
 to work fine..
 
 Any ideas?
 
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Re: [LARTC] Changing default route for an entire subnet/NIC

[Martin A. Brown]

Brian,

 : Oops, made a mistake in my example,
 : I actually enter
 : ip rule add from 192.168.0.0/24 table John
 :
 : As soon as I do this, that subnet loses all contact with my firewall,
 : so it can't DHCP an address, do DNS servers, ping, anything..

Perhaps what you wish to do is copy the entire main routing table to the
table John [0] and then change the default route in that table.

Try:

   # copy_routing_table John
   # ip route change table John default via $OTHER_GATEWAY

This is a simple application of policy routing.  Another possibility is to
exclude 192.168.0.0/24 from the rule itself:

   # ip rule add from 192.168.0.0/24 table John
   # ip rule add from 192.168.0.0/24 to 192.168.0.0/24 table main

You may wish to consider adding the prio keyword explicitly.  See also
some documents I have written in which I attempt to explain the policy
routing system in plain terms [1].

Good luck,

-Martin

  [0] http://linux-ip.net/html/scripts/copy-routing-table.sh
  [1] http://linux-ip.net/html/ch-routing.html

-- 
Martin A. Brown --- SecurePipe, Inc. --- [EMAIL PROTECTED]

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